We can then tell OCaml to use the contents of that file like this: It is exactly the same as typing it in manually […] Errors and warnings will be reported as usual. Note that the #use command is not part of the OCaml language for expressions – it is just a command we are giving to OCaml.

One thing to add is that unlike in Haskell, we can’t put our type signatures in the same file. Apparently, there’s a separate “interface file” with a .mli extension, but I won’t worry about that yet.